1. Field of the Invention
The present invention relates to a transmission rate control method for controlling a transmission rate of uplink user data transmitted by a mobile station, and a radio network controller.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Referring to FIG. 3, the mobile communication system, to which the “Enhanced Uplink” is applied, is explained.
In step S2001, the mobile station UE is establishing a data connection (E-DPDCH) for transmitting the uplink user data with the radio network controller RNC via the cell #10.
In step S2002, when the reception power of a common pilot channel from the cell #20 become more than or equal to the predetermined value, the mobile station UE transmits measurement report to the radio network controller RNC.
In step S2003, the radio network controller RNC requests the cell #20 to establish synchronization of radio links for uplink between the mobile station UE and the cell #20, based on the transmitted measurement report.
To be more specific, the radio network controller RNC transmits, to the cell #20, a SHO setting request including SHO parameters. The SHO parameters includes a channelization code for identifying a channel configuration in the radio links for uplink, a scrambling code for identifying the mobile station UE, and a start time of the SHO.
In step S2004, the cell #20 transmits a SHO setting response for indicating that the cell #20 has received the SHO setting request.
In step S2005, the radio network controller RNC requests the mobile station UE to establish synchronization of radio links for downlink between the cell #20 and the mobile station UE.
To be more specific, the radio network controller RNC transmits, to the mobile station UE, a SHO setting request including the SHO parameters. The SHO parameters includes a channelization code for identifying a channel configuration in the radio links for downlink, a scrambling code for identifying the cell #20, and a start time of the SHO.
In step S2006, the mobile station UE transmits a SHO setting response for indicating that the mobile station UE has received the SHO setting request. The mobile station UE shifts from the Non-SHO state to the SHO state based on the SHO parameters. In step S2007, the mobile station becomes in the SHO state with the cell #10 and the cell #20.
Based on the above steps, the mobile station UE in the EUL is configured to connect to a plurality of cells simultaneously in the SHO state, so as to prevent the interruption of communication.
Here, with regard to a certain mobile station UE, a set of radio links established between the mobile station UE and the cell controlled by the radio base station Node B will be called as an “active set”.
The active set will be updated, for example, when the mobile station UE shifts between the Non-SHO state and the SHO state, or when the cells to which the mobile station UE establishes radio links are changed.
Generally, when the effects of interference to neighboring cells are considered, it is preferable to control the transmission rate of uplink user data of the mobile station UE, between during the SHO state and during the Non-SHO state, differently.
However, in the conventional mobile communication system to which the “Enhanced Uplink” is applied, the radio base station Node B, which controls each cell, cannot identify whether the mobile station UE establishing the radio links with each cell is during the SHO state or during the Non-SHO state.
Accordingly, there has been a problem that, in the conventional mobile communication system to which the EUL is applied, it is not possible to perform the transmission rate control of the uplink user data, based on whether the mobile station UE is during the SHO state or during the Non-SHO state.